so im newer to the engine, but I can see what's wrong.
greenbullet.x = player.x and greenbullet.y = player.y means that you're teleporting the sprite over to the player, at least thats what I think.
what I would do (I dont know gdscript so well, I do python but you can probably figure out what I mean) is this:
if greenBullet.x > player.x:
greenBullet.x + 10 (or 20 or however many pixels you want)
elif greenBullet.x < player.x:
greenBullet.x - 10 (or 20 or however many pixels you want).
greenBullet.x = greenBullet.x
do the same thing but replace x with y, and maybe that might work. not trying it out in Godot myself, but yeah.